Use JsStrategy, remove KernelBackendStrategy

tests/compiler/dart2js/kernel/compiler_helper.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Partial test that the closed world computed from [WorldImpact]s derived from
 // kernel is equivalent to the original computed from resolution.
 library dart2js.kernel.compiler_helper;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:compiler/compiler_new.dart';
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/common/names.dart';
 import 'package:compiler/src/common/tasks.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/elements/elements.dart';
-import 'package:compiler/src/kernel/element_map_impl.dart';
+import 'package:compiler/src/kernel/element_map.dart';
 import 'package:compiler/src/kernel/kernel_strategy.dart';
 import 'package:compiler/src/library_loader.dart';
 import 'package:compiler/src/universe/world_builder.dart';
 import 'package:compiler/src/util/util.dart';
 import 'package:expect/expect.dart';
 import 'package:kernel/ast.dart' as ir;
 import '../memory_compiler.dart';
 import '../../../../pkg/compiler/tool/generate_kernel.dart' as generate;
 
 typedef Future<Compiler> CompileFunction();
@@ skipping 33 matching lines @@
           entryPoint: uri,
           memorySourceFiles: memorySourceFiles,
           options: [
             Flags.analyzeOnly,
             Flags.enableAssertMessage,
             Flags.loadFromDill
           ]);
       ElementResolutionWorldBuilder.useInstantiationMap = true;
       compiler2.resolution.retainCachesForTesting = true;
       KernelFrontEndStrategy frontendStrategy = compiler2.frontendStrategy;
-      KernelToElementMapImpl elementMap = frontendStrategy.elementMap;
+      KernelToElementMapForImpact elementMap = frontendStrategy.elementMap;
       ir.Program program = new ir.Program(
           libraries:
               compiler.backend.kernelTask.kernel.libraryDependencies(uri));
       LibraryElement library = compiler.libraryLoader.lookupLibrary(uri);
       Expect.isNotNull(library, 'No library found for $uri');
       program.mainMethod = compiler.backend.kernelTask.kernel
           .functionToIr(library.findExported(Identifiers.main));
       compiler2.libraryLoader = new MemoryDillLibraryLoaderTask(
           elementMap, compiler2.reporter, compiler2.measurer, program);
       await compiler2.run(uri);
@@ skipping 25 matching lines @@
       entryPoint: entryPoint,
       memorySourceFiles: memorySourceFiles,
       options: [
         Flags.analyzeOnly,
         Flags.enableAssertMessage,
         Flags.loadFromDill
       ]);
   ElementResolutionWorldBuilder.useInstantiationMap = true;
   compiler2.resolution.retainCachesForTesting = true;
   KernelFrontEndStrategy frontendStrategy = compiler2.frontendStrategy;
-  KernelToElementMapImpl elementMap = frontendStrategy.elementMap;
+  KernelToElementMapForImpact elementMap = frontendStrategy.elementMap;
   compiler2.libraryLoader = new MemoryDillLibraryLoaderTask(
       elementMap,
       compiler2.reporter,
       compiler2.measurer,
       compiler.backend.kernelTask.program);
   await compiler2.run(entryPoint);
   return new Pair<Compiler, Compiler>(compiler, compiler2);
 }
 
 class MemoryDillLibraryLoaderTask extends DillLibraryLoaderTask {
   final ir.Program program;
 
-  MemoryDillLibraryLoaderTask(KernelToElementMapImpl elementMap,
+  MemoryDillLibraryLoaderTask(KernelToElementMapForImpact elementMap,
       DiagnosticReporter reporter, Measurer measurer, this.program)
       : super(elementMap, null, null, reporter, measurer);
 
   Future<LoadedLibraries> loadLibrary(Uri resolvedUri,
       {bool skipFileWithPartOfTag: false}) async {
     return createLoadedLibraries(program);
   }
 }
 
 Future createTemp(Uri entryPoint, Map<String, String> memorySourceFiles,
@@ skipping 39 matching lines @@
       options: [Flags.loadFromDill]..addAll(options),
       outputProvider: compilerOutput);
   ElementResolutionWorldBuilder.useInstantiationMap = true;
   compiler.resolution.retainCachesForTesting = true;
   if (beforeRun != null) {
     beforeRun(compiler);
   }
   await compiler.run(dillFile);
   return compiler;
 }